Subsea systems, such as those used in exploration and production of oil and gas, continue to increase in complexity. A subsea well can include sensors and actuators located at or below the sea floor. The sensors can be, for example, pressure sensors, temperature sensors, and erosion detectors. The actuators can be, for example, valves, pumps, and other flow control devices. Information from the sensors is commonly communicated with other subsea facilities and then communicated with or processed by equipment at a surface facility. Similarly, controls for the actuators commonly originate at a surface facility. Accordingly, communication is needed between the subsea devices and equipment at the surface. These devices may be spread over a wide area and may also be subject to harsh conditions such as high pressure and temperatures.
In offshore drilling and production operations, equipment is often subjected to harsh conditions thousands of feet under the sea surface with working temperatures of −50° F. to 350° F. with pressures of up to 15,000 psi. Subsea control and monitoring equipment commonly are used in connection with operations concerning the flow of fluid, typically oil or gas, out of a well. Flow lines are connected between subsea wells and production facilities, such as a floating platform or a storage ship or barge. Subsea equipment includes sensors and monitoring devices (such as pressure, temperature, corrosion, erosion, sand detection, flow rate, flow composition, valve and choke position feedback), and additional connection points for devices such as down hole pressure and temperature transducers. A typical control system monitors, measures, and responds based on sensor inputs and outputs control signals to control subsea devices. For example, a control system attached to a subsea tree controls down-hole safety valves. Functional and operational requirements of subsea equipment have become increasingly complex along with the sensing and monitoring equipment and control systems used to insure proper operation.
To connect the numerous and various sensing, monitoring and control equipment necessary to operate subsea equipment, harsh-environment connectors are used with electrical cables, optical fiber cables, or hybrid electro-optical cables. There exists a variety of wet-mate and dry-mate electrical and optical connectors that may be employed in subsea communication systems.
To facilitate communication between these underwater devices, and between different communication mediums and network types, systems and control device are employed to manage the subsea equipment. Subsea communication may be implemented by fiber optic, electrical, or hybrid optical-electric communication systems. Fiber optic communication systems typically employ one or more optical fibers, while electrical communication systems employ copper wire which may be implemented as a twisted pair. Communication between devices and pieces of equipment may be on a TCP/IP network and may be handled by one or more modems, switches, routers, and control apparatuses.
Controller area network (“CAN”) buses are used to interconnect sensors, actuators, controllers, and other devices in applications such as automobiles, industrial automation, and medical equipment. Many circuits and devices have been developed for CAN bus communications. However, current CAN bus based subsea systems face several limitations. Network size is restricted due to the impedance drop that results from connecting multiple electrical devices in parallel. Additionally, conventional driver components may not be suitable for long transmission lines. One system and method for controlling optical CAN bus systems is described in SYSTEMS AND METHODS FOR SUBSEA OPTICAL CAN BUSES, Xi, U.S. Pat. No. 9,057,846, issued Jun. 16, 2015, and one cable that may be used in such a system is described in SUBSEA ELECTRO-OPTICAL CONNECTOR UNIT FOR ELECTRO-OPTICAL ETHERENET TRANSMISSION SYSTEM, Nagengast et al., U.S. Pat. No. 8,734,026, issued May 27, 2014, both of which are hereby incorporated by reference in their entirety.
In a typical subsea communication network having a plurality of wellheads a large subsea control module is employed to manage and facilitate communications between one or more subsea devices and other equipment on the surface over a CAN bus network. These subsea devices and other equipment may include devices such as sensors, sensor modules, or other similar monitoring devices. These devices typically require both electrical power and an CAN bus signal in order to function and communicate with other devices, such as the subsea control module, on the CAN bus network. For example, a sensor monitoring pressure at a wellhead will need a CAN bus connection, which is typically an electrical connection, to send and receive data to other devices, such as a subsea control module, on the CAN bus network. The sensor will also need electrical power to operate. While sensors may be low or very low power devices drawing little current, battery power is typically not an option as replacing or re-charging batteries on a subsea sensor is not practical or efficient. Additionally, in many systems electrical power is not available at the location of the sensor and must be provided to the sensor from the subsea control module or a power module located at the subsea control module.
Problems exist with these typical configurations wherein electrical power is provided to the sensor from the subsea control module. First, when the sensor is at a great distance from the subsea control module providing electrical power over a conductive wire or cable may be costly. Laying a conductive wire or cable on the sea bed and connecting a conductive wire or cable to the sensor may be impractical over distances of hundreds of meters or even kilometers. A conductive wire or cable of that length would be expensive to produce, heavy, and costly to repair or replace. Additionally, the conductive wire or cable would typically be part of or comprise a larger cable that also included the CAN bus connection, typically a twisted pair electrical connection. Providing both the power and the signal in the same cable may cause electromagnetic interference, and both the power and CAN bus signal may experience signal or power loss over longer cable lengths. The interference and signal loss problems increase proportionally along with the length of the cable. Some existing systems have partially overcome this problem by transmitting the CAN bus signal as an optical signal over an optical fiber. However, these systems still rely on a conductive wire or cable to transmit electrical power to the sensor.
What is needed is a system or device for providing both electrical power and a CAN bus signal over a great distance without the use of a conductive wire or cable.